Add a new GetTlsUniqueChannelBinding method to SSLSocket, and implement nss version.

net/socket/socket_test_util.h

Index: net/socket/socket_test_util.h
diff --git a/net/socket/socket_test_util.h b/net/socket/socket_test_util.h
index 0c7e4cf18d6599ee205541f60d559a2a2604154d..9e34d8a8dd5a1ac34c5cb95b21e3649f179ec376 100644
--- a/net/socket/socket_test_util.h
+++ b/net/socket/socket_test_util.h
@@ -602,6 +602,7 @@ class MockClientSocket : public SSLClientSocket {
                                    const base::StringPiece& context,
                                    unsigned char* out,
                                    unsigned int outlen) OVERRIDE;
+  virtual int GetTLSUniqueChannelBinding(std::string* out) OVERRIDE;
   virtual NextProtoStatus GetNextProto(std::string* proto,
                                        std::string* server_protos) OVERRIDE;
   virtual ServerBoundCertService* GetServerBoundCertService() const OVERRIDE;